LIQUID-CRYSTALLINE POLYACETYLENES - SYNTHESIS AND PROPERTIES OF -[((4'-CYANO-4-BIPHENYLYL)OXY)CARBONYL]-1-ALKYNES)

It is generally believed that cyano functionality is ''toxic'' to the classical MoCl5- and WCl6-based metathesis catalysts, but we here pres ent such an example in which a group of cyano-containing acetylene mon omers are polymerized by the ''simple'' metal halides. The WCl6(-Ph4Sn ) catalysts in dioxane initiate the polymerizations of n-{[(4'-cyano-4 -biphenylyl)oxy]carbonyl}-1-alkynes (AnCN; n = 2, 3, 8), yielding poly mers (PAnCNs) with relatively narrow molecular weight distributions (M -w/M-n down to 1.3). The same metal-halide mixtures in toluene, howeve r, are generally ineffective in polymerizing AnCNs, suggesting that th e tungsten-oxo complexes are involved in the active center formation. The differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry analyses reveal that all the PAnCNs are mesom orphic, with the longer flexible spacer favoring the better ordering o f the mesogenic groups. PA2CN shows monotropic nematicity, PA3CN exhib its enantiotropic nematicity, and PA8CN displays enantiotropic smectic ity with an interdigitated molecular packing arrangement (s(Ad)) over a wide temperature range (ca. 110 degrees C). In-domain banded structu res within the s(Ad) layers of PA8CN are observed during the transit o f the batonnets to the focal-conic fan textures, and the formation of large scale band morphology is achieved by the application of shear fo rce to PA8CN in its liquid crystalline state.